It is a known phenomenon that an electrostrictive member made either of piezoelectric material which has an inverse piezoelectric effect upon polarization or of electrostrictive material which has a high dielectric constant and an electrostrictive effect without polarization gives rise to a strain when certain voltage is applied thereto. A displacement caused by such a strain is too small to find any practical applications.
In order to boost the displacement to some extent it has been proposed that a plurality of electrostrictive members are stacked in such a manner that all the members are connected electrically parallel to each other.
For example, U.S. Pat. No. 3,524,196 discloses a piezoelectric actuator which comprises a stack of piezoelectric elements arranged longitudinally of one another for acting cumulatively in series, alternate piezoelectric elements being piezoelectrically oppositely orientated and connected in opposite senses between two input terminals. In this U.S. Patent, there is provided levers for amplifying the movement produced by the piezoelectric elements, each lever is carried on a body structure by a flexure hinge.
U.S. Pat. No. 3,614,486 discloses an actuator employing the inverse piezoelectric and electrostrictive effects in which it comprises a stack of piezoelectric discs which is placed between end blocks of conductive material and is retained in a supporting block.
Similar stack arrangement of ceramic or piezoelectric plates for providing a mechanical movement in response to applied electrical potentials is disclosed in U.S. Pat. Nos. 3,154,700 and 4,423,347.
In the previously proposed electrostriction actuators, however, the stack arrangement of piezoelectric elements or members requires relatively complicated operations for preparation and the total number and the total height of the piezoelectric members to be stacked are subject to limitations because of poor physical strength of the arrangement. Therefore, the conventional actuators of the type mentioned above do not necessarily produce a satisfactory displacement.
It is therefore an object of the present invention to provide an electrostrictive actuator which is compact and simplified, and capable of providing relatively large displacement.
Another object of the present invention is to provide to an electrostrictive actuator in which an supporting member for one or more electrostrictive elements is formed as means for amplifying the displacement produced by the electrostrictive elements.